The present invention relates to technology for performing inspection of surfaces of substrates used in the manufacture of liquid crystal devices or semiconductor wafers used in the manufacture of ICs, and in particular relates to an apparatus and method for performing so-called macro inspections in which the entire surface of the object is examined.
The macro inspection of the surfaces of the substrates used in the manufacture of liquid crystal devices and the semiconductor wafers used in the manufacture of ICs (hereinafter these items may also be described as the xe2x80x98objectxe2x80x99) refers to a visual inspection of the entire surface of the object. This inspection is performed to detect scratches or marks on the surface of the substrate or wafer, irregularities in the resist coating, or defects arising during the photolithography process. In conventional macro inspections, a spot light type white diffuse light source illuminates the object being rotated, and visual judgement by an examiner is performed to inspect the above-mentioned defects.
However, visual judgment by an examiner results in a variation in the level of inspection due to factors such as the difference in technical skill level between individual examiners and the physical condition of the examiner. This results in problems such as inefficiency and unstable inspection results. Furthermore, in the manufacture of substrates for liquid crystal devices and of wafers for ICs, because any surface contamination must be avoided, inspection processes performed by humans, which are one of the major causes of dust contamination, need to be avoided as much as possible.
As a result of the above-described situation, automated macro inspection processes have been proposed, such as the apparatus presented in Japanese Patent Application, Second Publication No. Hei 6-8789. In this apparatus, the surface of a wafer is illuminated with light and the reflected light therefrom is received via an ITV camera, and a surface defect inspection on the object is performed by comparing the reflected light image with a pre-recorded reflected light image of an object without defects. Because the field of view of the camera is smaller than the object, the object can be moved for inspection of the whole of the whole of the object. Furthermore, in this apparatus, in order to enable inspection under various illumination angles with respect to the object surface, the ITV camera is held in a stationary position and the angle of the object is varied.
However with the above type of surface inspection apparatus, a mechanism for setting the illumination angle is required, and when the mechanism is activated, dust may be generated by the moving parts of the mechanism, leading to the possibility of unwanted contamination of the surface of the object. The apparatus proposed in the aforementioned Japanese Patent Application performs macro inspections by using the light directly reflected off the surface of the object, and the camera is located so that the incident angle of the irradiated light on the surface of the object is equal to the reflection angle of the reflected light.
However, recently, the use of diffracted light or scattered light generated in accordance with the repeating pattern on the surface of the object has been investigated for use in surface inspection. In such a case, because the reception angle of the light from the object will vary due to factors such as the pattern pitch of the object, it is necessary to adjust the illumination angle of the illumination apparatus and the light reception angle of the image pick-up camera. Consequently, this case also requires a mechanism for adjusting the angles of illumination and reception, which generates dust and leads to the problem of unwanted contamination of the surface of the object.
In another case, Japanese Patent Application, First Publication No. Hei 8-75661 proposes an automatic inspection apparatus which is configured so that light from a light source is irradiated on to the object such as a wafer, and detection is performed by a single light reception optical system. With such an inspection apparatus, in the case where diffracted light from the object is to be detected, the diffraction angle will vary depending on the pattern pitch. Therefore, with wafers such as memory elements in which the elements are formed in a uniform pitch across the entire surface of the wafer, the inspection can be performed with a single measurement. However, in the case of CPU or ASIC (Application Specified IC) wafers where a variety of different types of elements are grouped together in different regions, the pattern pitch will differ for each of the regions, and therefore portions of the surface cannot be examined because no diffracted light is generated. Moreover, when an inspection is attempted on an object in which the pattern has been resist coated, the amount of diffracted light will vary considerably because the interference caused by the resist film will be heavily influenced by irregularities in the thickness of the film. Therefore, even thickness irregularities which have almost no effect on the process will be sufficient to cause the detection of a defect. Cases where the thickness of the resist is asymmetrical are particularly problematic, because the diffracted light image is very likely to develop irregularities and it is almost impossible to obtain a reliable inspection.
It is an object of the first embodiment of the present invention to provide a surface inspection apparatus which is able to efficiently carry out macro inspections on a variety of objects without requiring the variable adjustment of the illumination angle, the surface angle of the object, or the light reception angle for the light reception apparatus or image projection apparatus, that is, by maintaining the illumination apparatus and the image projection apparatus in fixed positions.
In order to achieve the above object, a first surface inspection apparatus according to the present invention (also referred to as a macro inspection apparatus) is characterized by comprising an illumination apparatus which is fixed in a position facing the object at a first predetermined angle with respect to the object and which irradiates an illuminating light beam which is a substantially parallel light beam, on to the inspection region of the object; an image projection apparatus which is fixed in a position facing the object at a second predetermined angle with respect to the object and which receives the diffracted light or scattered light generated from the illumination of the object by the aforementioned illuminating light beam and creates an image for the object; an image processing apparatus which is connected to the image projection apparatus and which takes the image signal obtained by the image projection apparatus and performs an inspection of the aforementioned inspection region by carrying out certain image processing; and a wavelength alteration member which is positioned within the optical path of the aforementioned illuminating light beam for altering the wavelength of the illuminating light. The operation of the apparatus may also be automated.
With a surface inspection apparatus of this construction, the wavelength of the illuminating light beam can be varied using the wavelength alteration member. Therefore, highly efficient macro inspection can be achieved by setting the wavelength so that the direction of the diffracted light or scattered light generated from the inspection region of the object coincides with the light reception direction of the image projection apparatus. Thus with this macro inspection apparatus, the illumination apparatus and the image projection apparatus can be fixed, making the provision of conventional moving mechanisms for altering the orientation of the illumination and image projection apparatus unnecessary, and hence reducing the generation of unnecessary dust and suppressing contamination of the object.
The illumination apparatus preferably has a diffuse light source and an optical member for converting the light from the light source into a substantially parallel light beam The aforementioned wavelength alteration member is preferably positioned between the diffuse light source and the optical member. In this situation, it is preferable for the optical member to have a concave mirror with the diffuse light source positioned at the focal point thereof. By using a concave mirror in this manner, the problem of chromatic aberration does not arise even in the case of illumination with white light.
Furthermore, for the same reasons, it is preferable for the image projection apparatus to have a concave mirror for converging the diffracted light or scattered light from the object, and an image pickup device for projecting an image of the object based on the converged light from the concave mirror.
The illumination apparatus can also have a linear diffuse light source and a cylindrical lens positioned facing along the line of the linear diffuse light source. In such a case, from the light from the linear diffusion source, the cylindrical lens generates a light beam which is substantially parallel in at least one direction and then illuminates the object. This type of construction allows the production of small scale, compact apparatuses at low cost.
The setting of the wavelength by the wavelength alteration member is carried out in the manner described below. In the case where the aforementioned first predetermined angle is represented by an angle of xcex8i with respect to a line perpendicular to the surface of the object, and the second predetermined angle is represented by an angle of xcex8d with respect to a line perpendicular to the surface of the object, then the wavelength xcex of the illuminating light beam is set so as to satisfy the following formula (1).
(sin xcex8ixe2x88x92sin xcex8d)=nxc2x7xcex/pxe2x80x83xe2x80x83(1)
(n: order of diffracted light undergoing image projection, p: pattern pitch of the surface of the object)
If the wavelength xcex of the illuminating light beam is set according to the above formula, then the image projection apparatus is able to efficiently capture diffracted light of order n, and the macro inspection utilizing this diffracted light can also be carried out efficiently.
In the case where a macro inspection is performed by capturing scattered light (rather than diffracted light) with the image projection apparatus, the setting of the wavelength by the wavelength alteration member is carried out in the manner described below. In the case where the first predetermined angle is represented by an angle of xcex8i with respect to a line perpendicular to the surface of the object, the second predetermined angle is represented by an angle of xcex8d with respect to a line perpendicular to the surface of the object, and the wavelength of the illuminating light beam which is set by the wavelength alteration member is represented by xcex, then the wavelength xcex of the illuminating light beam is set by the wavelength alteration member so that the value of xcex8d satisfies the requirement xcex8dxe2x80x2 less than xcex8d less than xcex8dxe2x80x3, where xcex8dxe2x80x2 is determined by the formula (2), and xcex8dxe2x80x3 is determined by the formula (3).
(sin xcex8ixe2x88x92sin xcex8dxe2x80x2)=nxc2x7xcex/pxe2x80x83xe2x80x83(2)
(sin xcex8ixe2x88x92sin xcex8dxe2x80x3)=(n+1)xc2x7xcex/pxe2x80x83xe2x80x83(3)
(n: order of the diffracted light generated from the illuminating light beam, p: pattern pitch of the surface of the object).
If the wavelength xcex of the illuminating light beam is set according to the above formulae, then the image projection apparatus is positioned between the direction of diffracted light of order n and the direction of diffracted light of order (n+1), meaning that no diffracted light will enter the image projection apparatus and only scattered light will be received. Consequently, macro inspection utilizing the scattered light can be carried out efficiently.
In order to achieve the above object, a second surface inspection apparatus according to the present invention, as shown in FIG. 9 comprises a first light reception optical system for receiving a first light beam (diffracted light or scattered light) from the surface; a second light reception optical system for receiving a second light beam (diffracted light or scattered light) from the surface; a first image processing apparatus for processing the image of the surface generated by the first light reception optical system; a second image processing apparatus for processing the image of the surface generated by the second light reception optical system, and a central computing device for detecting the condition of the surface by processing the information generated by the first and second image processing apparatus.
The second embodiment of the present invention is able to provide a surface inspection apparatus and a surface inspection method which enable highly reliable inspections to be performed regardless of the condition of the surface.
With the above construction, a first light beam (diffracted light or scattered light) from the surface is received by the first light reception optical system, and the surface image thus produced is processed by the first image processing apparatus. In the same way, a second light beam (diffracted light or scattered light) from the surface is received by the second light reception optical system, and the surface image thus produced is processed by the second image processing apparatus. Then, the condition of the surface is detected by processing the information generated by the two image processing apparatuses using the central computing device. The provision of the central computing device makes it possible to detect surface conditions which could not be distinguished from only a single set of information, by enabling the superimposition of two sets of data and subsequent addition or subtraction operations to be performed.
In such a case, it is also possible to provide an illumination optical system for illuminating the surface, and then positioning the optical axes of the first and second light reception optical systems in a substantially symmetrical manner with respect to the optical axis of the illumination optical system.
Furthermore, it is possible to project the illuminating light beam obliquely, and to position the light reception optical systems symmetrically for receiving the diffracted light from the intersecting pattern formed on the surface. Alternatively, it is possible to project the illuminating light beam substantially perpendicularly on to the surface, and to position the light reception optical systems symmetrically for receiving diffracted light from the pattern of order xc2x1n (where n is an integer).
With such an apparatus, in order to enable reception by the aforementioned first and second light reception optical systems of the diffracted light or scattered light generated in accordance with the structure of a body located on the aforementioned surface, the surface incorporating the optical axis of the first light reception optical system and the normal line H of the surface may intersect with the surface incorporating the optical axis of the second light reception optical system and the normal line H of the surface.
With such a construction, a light reception optical system is provided for which the optical axis lies within the intersecting surfaces, and so for example the two different directions of diffracted light generated from a semiconductor substrate, in which a pair of line and space patterns intersect one another, can be received simultaneously. Depending on the process, there are cases in which the direction of the diffracted light produced is not necessarily constant. This is because in memory elements and the like, line and space patterns are frequently positioned so as to intersect, and the diffracted light will typically be generated in a direction perpendicular to the lines. In such cases, with light reception systems which can accommodate only one direction of diffracted light, the wafer needs to be rotated to enable the diffracted light to be captured. This can result in an undesirable reduction in processing time, but with a construction of the present invention the two directions can be measured simultaneously. The patterns do not necessarily intersect orthogonally and so the light reception systems should be positioned in accordance with the pattern, in the direction of the generated diffracted light. However, orthogonal intersections are frequent, as in the case of a pair of line and space patterns which intersect orthogonally. In such cases, light reception optical systems having optical axes within the orthogonally intersecting surfaces should be provided.
A surface inspection method according to the present invention comprises an illumination step for illuminating the surface to be measured; a first light reception step for receiving a light beam (diffracted light or scattered light) of a first direction produced at the surface which has been illuminated via the illumination step; a second light reception step for receiving a light beam (diffracted light or scattered light) of a second direction produced at the surface which has been illuminated via the illumination step; a first image processing step for processing the image of the surface generated by the first light reception step; a second image processing step for processing the image of the surface generated by the second light reception step; and a step for detecting the condition of the surface by processing the information generated by the first and second image processing steps.
With such a construction, the surface is illuminated at the illumination step which produces diffracted light or scattered light. Because steps are provided for receiving light of both the first and second directions, a plurality of images are obtained. An image-processing step is provided for each of the different light directions therefore, for example, the plurality of images can be combined and then processed centrally.
With this method, using an example in which the pattern formed on the surface is a line and space pattern with an associated periodicity, and the aforementioned first and second light beams are a diffracted light beam of a first direction and a diffracted light beam of a second direction respectively, then each of the directions can be set as those directions substantially perpendicular to the lines of the aforementioned line and space patterns. For semiconductor devices, frequently the line and space patterns are formed so as to intersect orthogonally, but if the first and second directions are chosen so as to be substantially perpendicular with respect to the lines of the respective line and space patterns, then the diffracted light from each pattern can be received at the first and second directions.
Furthermore, with the method of the present invention, the aforementioned first and second directions could also be set to the traveling direction of diffracted light of order plus 1 and diffracted light of order minus 1 from the aforementioned line and space patterns. In such a case, the first and second directions correspond with the direction of the diffracted light of order xc2x11, enabling information to be obtained on symmetrical directions related to the surface.
In a second surface inspection method according to the present invention, the wavelength of the illuminating light beam is altered, the surface is illuminated with the illuminating light beam of altered wavelength, and an inspection of the surface is performed based on reflected light from the surface.
With such a method, illumination with an illuminating light beam of altered wavelength provides a plurality of images which can, for example, be combined and a surface inspection can then carried out centrally.
A third surface inspection apparatus according to the present invention comprises an illumination apparatus which is positioned in a predetermined position relative to the surface and which illuminates the surface with an illuminating light beam; a wavelength alteration member which can be moved in and out of the optical path of the illuminating light beam and which alters the wavelength of the illuminating light beam; and a light reception apparatus which is positioned in a predetermined location relative to the surface and which receives light from the surface produced by illumination with the wavelength altered illuminating light beam. With this type of apparatus, a plurality of images are obtained by illumination with the illuminating light beam of altered wavelength, and they can, for example, be combined and a surface inspection carried out centrally.
Furthermore, a method for assembling a surface inspection apparatus according to the present invention involves positioning the illumination apparatus, which illuminates the surface with an illuminating light beam, in a predetermined location relative to the surface, positioning the wavelength alteration member, which alters the wavelength of the illuminating light beam, so as to enable movement in and out of the optical path of the illuminating light beam, and positioning the light reception apparatus, which receives light from the surface produced by illumination with the wavelength altered illuminating light beam, in a predetermined location relative to the surface.